Strictly speaking, I don't believe that there is such a thing as a "genuine" rack. These were sold by some Honda dealers back in the early `70s, but to the best of my knowledge they were aftermarket...like buddy pegs.
The link takes you to a vendor who sells what is generally considered the "correct" style. These are available from other vendors as well. The "original" type uses the rear fender and shock mounts as the attaching points and locates the tail light bracket atop the fender mount. The photo in this thread is of a Chinese rack made for a clone bike; it may fit with some minor mods. As you can see in the pic, the Chinese rack uses the shock mounts and rear frame holes as attaching points. Not sure which is "better", that call is up to the individual. However, the main tradeoff seems to be size of the platform (the CT rack is larger) vs a vertical bar and more tie-down points. That vertical bar is more useful than you might think, especially for carrying a gas can securely.